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Figure 1.
Characterization of Antibodies Against the α-Amino-3-Hydroxy-5-Methyl-4-Isoxazolepropionic Acid (AMPA) Receptor
Characterization of Antibodies Against the α-Amino-3-Hydroxy-5-Methyl-4-Isoxazolepropionic Acid (AMPA) Receptor

A, Sagittal section of a rat brain incubated with cerebrospinal fluid (CSF) from a patient with encephalitis associated with antibodies against the AMPA receptor showed intense reactivity of the hippocampus, subiculum, basal ganglia, and molecular layer of the cerebellar cortex. D, HEK293 cells expressing the AMPA receptor (GluR1 and GluR2) reacted with CSF from the same patient. C, E, and F, This reactivity colocalized (E) with the reactivity of a monoclonal rabbit antibody against GluR1 (C and F). B, F, and H, No reactivity was observed with CSF from a control subject. In A and B, the cell nuclei were stained with 4’,6-diamidino-2-phenylindole. In D and G, GluR1 was labeled with a monoclonal rabbit antibody (04-855; Millipore). Immunofluorescence magnification ×2.5 for A and B and ×400 for C through H.

Figure 2.
Diffuse Cortical Atrophy in Encephalitis Associated With Antibodies Against the α-Amino-3-Hydroxy-5-Methyl-4-Isoxazolepropionic Acid Receptor
Diffuse Cortical Atrophy in Encephalitis Associated With Antibodies Against the α-Amino-3-Hydroxy-5-Methyl-4-Isoxazolepropionic Acid Receptor

Brain magnetic resonance imaging (axial fluid-attenuated inversion recovery sequences) at disease onset (left) and after 2 months (right) in a patient with the fulminant encephalitis mode of onset. Note the initial hyperintensity of the left insular cortex (arrowhead) and the rapid severe and diffuse parenchymal atrophy.

Table 1.  
Clinical Features and Outcomes in 7 Patients With Encephalitis Associated With Antibodies Against the α-Amino-3-Hydroxy-5-Methyl-4-Isoxazolepropionic Acid Receptor
Clinical Features and Outcomes in 7 Patients With Encephalitis Associated With Antibodies Against the α-Amino-3-Hydroxy-5-Methyl-4-Isoxazolepropionic Acid Receptor
Table 2.  
Ancillary Data and Outcomes in 18 Previously Described Patients With Encephalitis Associated With Antibodies Against the α-Amino-3-Hydroxy-5-Methyl-4-Isoxazolepropionic Acid Receptor
Ancillary Data and Outcomes in 18 Previously Described Patients With Encephalitis Associated With Antibodies Against the α-Amino-3-Hydroxy-5-Methyl-4-Isoxazolepropionic Acid Receptor25,7,8
1.
Leypoldt  F, Armangue  T, Dalmau  J.  Autoimmune encephalopathies. Ann N Y Acad Sci. 2015;1338:94-114.
PubMedArticle
2.
Lai  M, Hughes  EG, Peng  X,  et al.  AMPA receptor antibodies in limbic encephalitis alter synaptic receptor location. Ann Neurol. 2009;65(4):424-434.
PubMedArticle
3.
Graus  F, Boronat  A, Xifró  X,  et al.  The expanding clinical profile of anti-AMPA receptor encephalitis. Neurology. 2010;74(10):857-859.
PubMedArticle
4.
Bataller  L, Galiano  R, García-Escrig  M,  et al.  Reversible paraneoplastic limbic encephalitis associated with antibodies to the AMPA receptor. Neurology. 2010;74(3):265-267.
PubMedArticle
5.
Wei  YC, Liu  CH, Lin  JJ,  et al.  Rapid progression and brain atrophy in anti-AMPA receptor encephalitis. J Neuroimmunol. 2013;261(1-2):129-133.
PubMedArticle
6.
Gleichman  AJ, Panzer  JA, Baumann  BH, Dalmau  J, Lynch  DR.  Antigenic and mechanistic characterization of anti-AMPA receptor encephalitis. Ann Clin Transl Neurol. 2014;1(3):180-189.
PubMedArticle
7.
Spatola  M, Stojanova  V, Prior  JO, Dalmau  J, Rossetti  AO.  Serial brain ¹⁸FDG-PET in anti-AMPA receptor limbic encephalitis. J Neuroimmunol. 2014;271(1-2):53-55.
PubMedArticle
8.
Dogan Onugoren  M, Deuretzbacher  D, Haensch  CA,  et al.  Limbic encephalitis due to GABAB and AMPA receptor antibodies: a case series [published online October 9, 2014]. J Neurol Neurosurg Psychiatry. 2014;jnnp-2014-308814.
PubMed
9.
Dalmau  J, Rosenfeld  MR.  Paraneoplastic syndromes of the CNS. Lancet Neurol. 2008;7(4):327-340.
PubMedArticle
10.
Saiz  A, Blanco  Y, Sabater  L,  et al.  Spectrum of neurological syndromes associated with glutamic acid decarboxylase antibodies: diagnostic clues for this association. Brain. 2008;131(pt 10):2553-2563.
PubMedArticle
11.
Malter  MP, Frisch  C, Schoene-Bake  JC,  et al.  Outcome of limbic encephalitis with VGKC-complex antibodies: relation to antigenic specificity. J Neurol. 2014;261(9):1695-1705.
PubMedArticle
12.
Bien  CG, Vincent  A, Barnett  MH,  et al.  Immunopathology of autoantibody-associated encephalitides: clues for pathogenesis. Brain. 2012;135(pt 5):1622-1638.
PubMedArticle
13.
Wagner  J, Witt  JA, Helmstaedter  C,  et al.  Automated volumetry of the mesiotemporal structures in antibody-associated limbic encephalitis. J Neurol Neurosurg Psychiatry. 2015;86(7):735-742.
PubMedArticle
14.
Dalmau  J, Lancaster  E, Martinez-Hernandez  E, Rosenfeld  MR, Balice-Gordon  R.  Clinical experience and laboratory investigations in patients with anti-NMDAR encephalitis. Lancet Neurol. 2011;10(1):63-74.
PubMedArticle
15.
Martinez-Hernandez  E, Horvath  J, Shiloh-Malawsky  Y, Sangha  N, Martinez-Lage  M, Dalmau  J.  Analysis of complement and plasma cells in the brain of patients with anti-NMDAR encephalitis. Neurology. 2011;77(6):589-593.
PubMedArticle
16.
Camdessanché  JP, Streichenberger  N, Cavillon  G,  et al.  Brain immunohistopathological study in a patient with anti-NMDAR encephalitis. Eur J Neurol. 2011;18(6):929-931.
PubMedArticle
17.
Peng  X, Hughes  EG, Moscato  EH, Parsons  TD, Dalmau  J, Balice-Gordon  RJ.  Cellular plasticity induced by anti–α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor encephalitis antibodies. Ann Neurol. 2015;77(3):381-398.
PubMedArticle
18.
Ha  JC, Richman  DP.  Myasthenia gravis and related disorders: pathology and molecular pathogenesis. Biochim Biophys Acta. 2015;1852(4):651-657.
PubMedArticle
19.
Prüss  H, Finke  C, Höltje  M,  et al.  N-methyl-d-aspartate receptor antibodies in herpes simplex encephalitis. Ann Neurol. 2012;72(6):902-911.
PubMedArticle
20.
Feichtinger  M, Wiendl  H, Körner  E,  et al.  No effect of immunomodulatory therapy in focal epilepsy with positive glutamate receptor type 3–antibodies. Seizure. 2006;15(5):350-354.
PubMedArticle
Original Investigation
October 2015

Clinical Spectrum of Encephalitis Associated With Antibodies Against the α-Amino-3-Hydroxy-5-Methyl-4-Isoxazolepropionic Acid ReceptorCase Series and Review of the Literature

Author Affiliations
  • 1Université Claude Bernard Lyon 1, Lyon, France
  • 2Institut National de la Santé et de la Recherche Médicale (INSERM) et Centre National de la Recherche Scientifique (CNRS), Equipe Neuro-oncologie et Neuro-inflammation, Centre de Recherche en Neurosciences de Lyon, Unités Mixtes de Recherche INSERM S1028 et CNRS 5292, Lyon, France
  • 3Hospices Civils de Lyon, Service de Neuro-oncologie, Hôpital Neurologique Pierre Wertheimer, Lyon, France
  • 4Faculté de Médecine, Université Paris-Est Créteil Val de Marne, Créteil, France
  • 5Service de Neurologie, Centre Hospitalier Universitaire Henri Mondor, Créteil, France
  • 6Centre National de Référence pour les Syndromes Neurologiques Paranéoplasiques, Lyon, France
  • 7Département de Neurologie, Centre Hospitalier Universitaire de Toulouse, Hôpital Pierre-Paul Riquet, Toulouse, France
  • 8Pôle Neurosciences, Centre Hospitalier Universitaire de Dijon, Dijon, France
  • 9Département de Neurologie, Groupe Hospitalier Pitié-Salpêtrière, Paris, France
  • 10Service de Neurologie, Centre Hospitalier Universitaire de Saint-Étienne, Hôpital Bellevue, Saint-Étienne, France
JAMA Neurol. 2015;72(10):1163-1169. doi:10.1001/jamaneurol.2015.1715
Abstract

Importance  The clinical features of autoimmune encephalitis associated with antibodies against the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR-Abs) remain poorly defined.

Objectives  To describe 7 patients with encephalitis and AMPAR-Abs and to provide a review of the literature on this disease entity.

Design, Setting, and Participants  The setting was the Centre National de Référence pour les Syndromes Neurologiques Paranéoplasiques (Lyon, France), and participants were 7 consecutive patients diagnosed as having encephalitis and AMPAR-Abs between January 1, 2010, and December 1, 2014. Patients’ clinical data were analyzed, with a median follow-up period of 12 months (range, 2-31 months). Relevant articles were identified in the MEDLINE database using the keywords autoimmune encephalitis and AMPA receptor antibodies until February 15, 2015.

Main Outcomes and Measures  Modes of onset, full clinical presentations, and cancer prevalence.

Results  The patients included 4 women and 3 men (median age, 56 years). Four main modes of encephalitis onset were observed, including confusion (3 patients), epileptic (1 patient), amnestic (1 patient), and a severe form of fulminant encephalitis (2 patients). In contrast with previous reports, we observed only 1 patient with seizures. Two patients had cancer (1 lung carcinoma and the other thymic carcinoma). Analysis of the literature identified 35 published cases of encephalitis and AMPAR-Abs, including 18 with clinical data. The same modes of encephalitis onset were observed, including confusion (12 patients), epileptic (1 patient), amnestic (3 patients), and fulminant encephalitis (2 patients). Eleven patients were initially seen with a neoplasm (lung, breast, thymoma, or ovary).

Conclusions and Relevance  The clinical spectrum of AMPAR encephalitis is variable. Cancer was found in 13 of 27 patients (48%) with known cancer status. Most patients are seen with symptoms suggestive of autoimmune limbic encephalitis, although they can be paucisymptomatic or may manifest severe panencephalitis that evolves to a minimally conscious state and diffuse cortical atrophy. Patients suspected of having autoimmune encephalitis should undergo screening for serum and cerebrospinal fluid AMPAR-Abs.

Introduction

Autoimmune synaptic encephalitides are neurological disorders associated with autoantibodies that target neuronal surface proteins and alter synaptic transmission in a dose-dependent, reversible, and selective manner.1 They constitute an expanding disease entity of great interest over recent years because of the novelty of their pathogenetic mechanisms and their potential reversibility with adequate immunotherapy. Among them, autoimmune encephalitis associated with antibodies against the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR-Abs) (hereafter AMPAR-E) has been described in a cohort of 10 patients.2 Analysis of the clinical features of this initial series of patients suggested a mainly paraneoplastic autoimmune encephalitis occurring mostly in middle-aged women that is prone to relapse and is particularly epileptogenic. However, several series and case reports have recently expanded this view.38 Therefore, the clinical phenotype associated with AMPAR-E, as well as the vital and functional prognosis of patients with this disease entity, is unclear. To clarify the clinical features of AMPAR-E, we herein report and analyze the clinical features of 7 patients with AMPAR-E diagnosed at the Centre National de Référence pour les Syndromes Neurologiques Paranéoplasiques (Lyon, France) and perform a review of the literature in light of these 7 cases.

Methods

All patients for whom cerebrospinal fluid (CSF) samples were studied in the National Reference Center for Paraneoplastic Neurological Diseases between January 1, 2010, and December 1, 2014, and who were positive for autoantibodies directed against the GluR1 and GluR2 subunits of the AMPA receptor were included in the study. Written informed consent was obtained from all patients, and the study was approved by the institutional review board of Université Claude Bernard Lyon 1 and Hospices Civils de Lyon.

The AMPAR-Abs were screened using indirect immunofluorescence assays on rat brain hippocampus histological sections and cell-based assays on cultured HEK293 cells. Briefly, sagittal sections from adult rats were produced using a cryostat microtome (CM1520; Leica Biosystems). After saturation, diluted CSF (1:10) was incubated overnight at 4°C. Patient antineuronal immunoglobulin G (IgG) was identified using a fluorescent antihuman IgG commercial antibody (A-20980; Invitrogen). Immunostaining was suggestive for AMPAR-Abs when primary reactivity was observed with the neuropil of the hippocampus, subiculum, caudate, and striatum and the cerebellar molecular layer2 (Figure 1). In parallel, cultured HEK293 cells were transfected with plasmids containing the genes coding for the GluR1 and GluR2 subunits of the AMPA receptor using a plasmid transfection reagent (Lipofectamine LTX; Invitrogen). After saturation, diluted CSF (1:10) was added to the transfected cells for 3 hours at room temperature. Cells were then fixed with 1% paraformaldehyde, and AMPAR-Abs were identified using the fluorescent antihuman IgG commercial antibody. Subsequently, we screened the serum samples of all patients who were positive for CSF AMPAR-Abs using the same protocol. Serum and CSF samples were deposited in the collection of biological samples registered as the Neurobiotec biobank of the Hospices Civils de Lyon (Lyon, France).

Clinical and ancillary data of patients who were positive for AMPAR-Abs were obtained by telephone or email at the time of the biological sample diagnosis and at least twice a year to assess the early disease stage and further clinical evolution. Patient characteristics were compiled, focusing on age, sex, medical history, and associated neoplasms. Clinical events were classified as cognitive dysfunction (including memory impairment, dysexecutive features, apraxia, and aphasia), psychiatric manifestations, confusion, behavioral disturbances, seizures, focal neurological deficits, sleep disorders, and alteration of vigilance. Outcomes were assessed using the modified Rankin Scale (mRS), administered every 3 months. Ancillary test results were compiled, with a particular focus on brain magnetic resonance imaging (MRI), scalp electroencephalogram (EEG), CSF analysis, other autoantibodies in serum or CSF samples, and oncological screening. Treatment modalities of immunotherapy and oncological therapy were recorded.

To identify relevant publications regarding AMPAR-E, we searched the MEDLINE database using the keywords autoimmune encephalitis and AMPA receptor antibodies. The search was periodically repeated until February 15, 2015. Reported cases were analyzed, with a focus on the initial clinical and ancillary presentation, cancer and immunological background, immunotherapy, and clinical evolution.

Results
Clinical Findings

We identified 7 patients with AMPAR-Abs, including 4 women and 3 men (complete clinical vignettes are given in the eAppendix in the Supplement). Their median age was 56 years (range, 21-92 years). All patients were positive for AMPAR-Abs in both serum and CSF samples (antibody titer range, 1:20 to greater than 1:360).

The onset of AMPAR-E was acute in all patients. Patients had cognitive alterations such as anterograde memory deficits (7 patients), dysexecutive symptoms (5 patients), and confusion (5 patients). Other frequent features were insomnia (4 patients), cerebellar signs (4 patients), headache (3 patients), oculomotor disorders (3 patients), motor deficits (2 patients), depression or delusion (2 patients), alteration of vigilance (2 patients), and movement disorders (1 patient). Seizures were observed in only 1 patient. Two patients had cancer (one lung carcinoma and the other thymic carcinoma), and another patient had thymus hyperplasia.

Based on the prominent clinical feature at admission, the following 4 main modes of AMPAR-E onset were observed: (1) confusion, (2) isolated epileptic, (3) isolated amnestic, and (4) a severe form of fulminant encephalitis. Clinical and ancillary data and outcomes for each mode of onset are summarized in Table 1. Alternative infectious, metabolic, or iatrogenic causes of encephalitis were ruled out in all patients.

Among 3 patients who were initially seen with confusion (median age, 58 years), one also had motor deficits, and another had nystagmus and cerebellar symptoms; none had seizures. One patient had concomitant anti-Hu antibodies, and oncological screening revealed a lesion suggestive of lung cancer.

One 43-year-old patient had de novo epilepsy as her only identifiable clinical feature at admission. She had experienced a sudden onset of daily temporomesial seizures and 1 month later manifested mild anterograde amnesia, discrete dysexecutive features, and mild cerebellar dysmetria. As such, her clinical presentation differed from that of the other patients in the series. Most important, she was positive for anti-Lgi1 and anti-GAD65 antibodies.

A purely amnestic syndrome was observed in 1 woman (age, 92 years). In this patient, mild anterograde amnesia was noted over a few days in the absence of fever, seizure, behavioral disturbances, or other neurological defects. She showed disorientation in space and time that was attributed to acute anterograde amnesia but demonstrated no other signs or symptoms, particularly no confusion.

In 2 patients (a 21-year-old woman and a 22-year-old man), encephalitis manifested as a fulminant course, with acute loss of consciousness, fever, diffuse hypertonia, and lateralized ocular deviation. Coma was preceded by reports of memory and cephalalgia deficits in both patients and by digestive symptoms (abdominal pain and nausea) in 1 patient. Both patients remained comatose for 4 weeks and then improved progressively. Confusion, behavioral disorders, dysexecutive symptoms, and psychiatric features were evident in both patients and preceded coma by 12 days in the female patient.

All patients were treated with intravenous IgG, combined with plasmapheresis or corticosteroids, within the first 6 weeks of the disease (median, 3 weeks from the onset). Additional therapeutic agents were rituximab (2 patients [375 mg/m2/wk]), cyclophosphamide (2 patients [1 g/mo]), and azathioprine sodium (1 patient [75 mg/d]). No relevant differences were observed regarding treatment modalities across the modes of AMPAR-E onset. When present, cancer was treated with chemotherapy (in both cases).

The median follow-up period was 12 months (range, 2-31 months). No relapse was observed in our patients. The median mRS score at the last visit was 3 (range, 0-6).

Differences in disease evolution were observed based on the mode of onset. Poor improvement was observed in the 3 patients whose mode of onset was confusion (median mRS score, 3 at the last visits at 2, 9, and 15 months, respectively), with all patients manifesting disabling cognitive sequelae in memory and executive functions. One patient had persistent right hemiparesis. Conversely, the patient with a new-onset epileptic mode of onset improved significantly (mRS score at the last visit, 1). She had complete control of seizures on a regimen of lacosamide only.

The patient with an amnestic pattern of onset remained stable at 6 months. Stabilization of her slight ataxia was noted. Finally, outcomes differed in the 2 patients with the comatose pattern of onset. While the man gradually improved (mRS score, 1 at the last visit at 18 months), the woman remained in a minimally conscious state for several months, with neurological examination demonstrating tetrapyramidal signs, sphincter dysfunction, movement disorders (hemidystonia, myoclonus, and oculogyric crisis), and downbeat nystagmus. She died of sepsis 12 months after disease onset, and no autopsy was performed.

All patients underwent brain MRI, scalp EEG, CSF analysis, and oncological screening (whole-body tomodensitometry or fluorodeoxyglucose positron emission tomography). Ancillary results are summarized in Table 1. Electroencephalographic examination was performed at the acute phase in all patients. Hyponatremia was observed in the patient with anti-Hu antibodies and in a patient with the fulminant encephalitis mode of onset, both of whom had documented cerebral salt-wasting syndrome.

Serial brain MRI revealed different patterns of disease evolution based on the clinical presentation. Bilateral temporomesial fluid-attenuated inversion recovery hyperintensities were observed on the initial MRI in all patients whose mode of onset was confusion or epileptic. However, at imaging 6 months after the onset, hyperintensities had resolved in 2 patients whose mode of onset was confusion (MRI was not performed in the third patient), with none or slight hippocampal atrophy. In the patient with an epileptic onset of disease, follow-up brain MRI at 6 months showed prominent right hippocampal sclerosis.

The brain MRI of the patient with isolated amnestic onset of disease was unremarkable. In the 2 patients with a fulminant encephalitis mode of onset, severity of brain MRI lesions appeared to correlate with clinical outcomes. The patient with a poor outcome had diffuse patchy T2-weighted hyperintensities and signs of cytotoxic edema on her initial brain MRI. The lesions evolved to diffuse and severe cortical atrophy 3 months later (Figure 2). Conversely, in the patient with a favorable outcome, brain MRI showed bilateral striatal intensities that resolved after 18 months of disease evolution.

Review of the Literature

To date, 35 patients with AMPAR-E have been described in 7 publications.28 Informative clinical data at disease onset were available for 18 of them.25,7,8 Oncological status was provided for 20 patients.25,7,8

Sixty-nine percent (22 of 32) of the cases occurred in women, and the median patient age was 56.5 years (range, 7-87 years).28 Cancer was found in 13 of 27 patients (48%) with known cancer status. Eleven of 20 patients (55%) had a neoplasm (4 lung cancers, 3 breast cancers, 2 thymus carcinomas, 1 thymoma, and 1 ovarian cancer). All described patients had cognitive alterations, including anterograde memory deficits (83% [15 of 18]), dysexecutive features (17% [3 of 18]), and confusion (72% [13 of 18]). Seizures were present in 33% (6 of 18) of patients. Less frequent features were sleep disorders, such as insomnia or hypersomnia (22% [4 of 18]), alteration of vigilance (17% [3 of 18]), cerebellar signs (17% [3 of 18]), nystagmus (17% [3 of 18]), fever (11% [2 of 18]), aphasia (6% [1 of 18]), and headache (6% [1 of 18]).

At admission, the disease presentations were confusion in 12 patients,24 epileptic in 1 patient,7 amnestic in 3 patients,8 and fulminant encephalitis in 2 patients.2,5 Ancillary results and outcomes based on clinical presentation are summarized in Table 2. Seventeen of 18 patients (94%) received immunotherapy: 9 were treated with combinations of corticosteroids, intravenous immunoglobulin, or plasmapheresis, and 8 were treated with corticosteroids or intravenous immunoglobulin only. Four patients were also administered long-term treatment with azathioprine because of the initial clinical severity or the occurrence of relapses. The median follow-up period was 16 months (range, 2 weeks to 120 months). Nine relapses occurred in 5 patients. The median mRS score at the last visit was 2 (range, 0-6), and the outcomes were heterogeneous. Fulminant encephalitis at presentation was associated with a poor recovery (death or severe sequelae).

Discussion

Clinical presentations at the onset of AMPAR-E were diverse, including behavioral, cognitive, motor, and sensory manifestations. Some of the symptoms observed (eg, memory deficits, cerebellar signs, or movement disorders) suggest involvement of the hippocampus, cerebellum, and basal ganglia, which are anatomical structures that were specifically stained by patient CSF when applied to histological sections of rat brains.2 The same regions were occasionally involved on brain MRI.2,5 Seizures, which were observed in 33% (6 of 18) of the previously published cases, were present in only 1 of our patients. Electroencephalographic examination, performed at the acute phase in all of our patients, detected no subclinical seizures.

We observed 4 main clinical presentations of AMPAR-E onset. Confusion was the most frequent feature, noted in 72% (13 of 18) of the reported cases. Most of the patients whose mode of onset was confusion had a presentation suggestive of autoimmune encephalitis, with behavioral disturbances, anterograde amnesia, and seizures.9 However, various extralimbic symptoms were observed, including dysexecutive features, movement disorders, cerebellar signs, sleep disorders, and alterations of consciousness.

In contrast, only 2 patients (including 1 in our case series) were seen with new-onset epilepsy as their only symptom at admission, and both recovered well. The cognitive alterations that developed secondarily may in part be due to subclinical seizures,7 and long-term antiepileptic treatment appears mandatory in such cases. Most important, our patient with an epileptic mode of onset had anti-GAD65 and anti-Lgi1 antibodies in addition to AMPAR-Abs. Anti-Lgi1 antibodies relate to a particularly epileptogenic autoimmune encephalitic syndrome, while anti-GAD65 antibodies are involved in epileptic and cerebellar ataxic autoimmune disorders.10,11 Both autoantibodies are associated with hippocampal atrophy.10,12 Therefore, it cannot be excluded that those autoantibodies had some role in the development of her symptoms and the hippocampal atrophy that followed.

One of our patients and 3 previously described patients were initially seen with acute amnesia as their prominent feature.8 Finally, 2 of our patients manifested a fulminant encephalitis form, with coma, fever, diffuse hypertonia, and ocular deviation. Among them, 1 patient had a dramatic evolution of her disease to rapid diffuse corticosubcortical atrophy. Wei et al5 described a similar presentation, and one of the patients in the initial series of AMPAR-E appeared to fit the same pattern, although the clinical data provided were incomplete.2 It is unknown why some patients develop this severe encephalitis and what causes such variability in outcomes. Moreover, this pattern is reminiscent of infectious encephalitis, emphasizing that autoimmune encephalitis should be considered in the differential diagnosis of any patient seen with acute febrile encephalitis of unclear origin.

Evolution of disease to hippocampal atrophy was observed in 2 of our patients and in 3 patients described in the literature, with diffuse cortical atrophy noted in 2 of 4 patients with a fulminant encephalitis pattern.5 Involvement of complement-mediated and antibody-dependent cell-mediated cytotoxicity has been suggested in anti-VGKC and anti-GAD65 encephalitis, 2 autoimmune conditions that frequently lead to hippocampal sclerosis.1113 In contrast, anti–N-methyl-d-aspartate receptor encephalitis does not result in cortical atrophy, and complement deposits were not found in the brains of patients with this form of encephalitis.1416 In addition to the functional effect of AMPAR-Abs that was demonstrated in vitro,2,6,17 one can assume that complement-mediated or antibody-dependent cell-mediated cytotoxicity might be involved in the pathogenic process underlying AMPAR-E, although histological and experimental data are lacking.

None of our patients relapsed, in contrast to the elevated frequency of relapsing patients in the literature. In some patients, the follow-up period was too short to observe relapses, although the relative precocity of immunotherapy initiation might have contributed to prevention. Nonetheless, the propensity of AMPAR-E to relapse is unclear, and long-term immunosuppression may be beneficial, as for other types of autoimmune encephalitis.

Neoplasms were found in 55% (11 of 20) of the previously published patients and in 2 of our patients, suggesting that AMPAR-E is not paraneoplastic in a significant proportion of cases. No difference in terms of clinical presentation was observed between patients with vs without cancer. Moreover, thymus abnormalities (eg, thymus hyperplasia, thymoma, and thymic carcinoma) were observed in 2 of our patients and in 3 of 20 (15%) previously published patients. As for other neurological immune diseases, alterations of the intrathymic mechanisms of tolerance induction could therefore be involved in the development of AMPAR-E.18 Apart from pathogenetic considerations, this observation stresses the importance of oncological screening in patients with AMPAR-E and raises the question of whether thymectomy should be proposed in nonparaneoplastic cases.

There are limitations to our study. The small sample sizes did not allow us to draw firm conclusions regarding clinical phenotypes that would specifically associate with this antibody. In addition, we did not assess the specificity of the GluR1 or GluR2 subunit of AMPAR-Abs in our patients. Even so, most of the previously described patients had antibodies against GluR2, and no obvious differences in terms of clinical presentation were observed between GluR2-reactive and GluR1-reactive patients, rendering antigenic specificity insufficient to explain the clinical diversity of AMPAR-E.2,4,5,8 Furthermore, antineuronal autoantibodies can be detected in the course of various nonautoimmune neurological diseases (eg, viral encephalitis or noninflammatory refractory epilepsy).19,20 Therefore, the finding of antineuronal autoantibodies, such as AMPAR-Abs does not necessarily imply that they are the cause of ongoing neurological disease. In daily practice, the significance of AMPAR-Abs has to be considered based on the clinical context after cautious exclusion of alternative diagnoses.

Conclusions

Our study demonstrates that AMPAR-E is heterogeneous in clinical presentation and severity. This case series and review of the literature emphasizes that, in addition to patients with classic features of limbic encephalitis, autoimmune encephalitis should be considered in patients with acute isolated amnesia, new-onset epilepsy, or fulminant encephalopathy. Moreover, AMPAR-Abs should be included in the comprehensive evaluation of serum and CSF samples from any patient suspected of having autoimmune encephalitis. In AMPAR-E, oncological screening is mandatory and should focus on the lung, breast, and thymus. If initiated early and continued on a long-term basis, immunotherapy may prevent relapse and improve outcomes.

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Article Information

Accepted for Publication: June 5, 2015.

Corresponding Author: Jérôme Honnorat, MD, PhD, Hospices Civils de Lyon, Service de Neuro-oncologie, Hôpital Neurologique Pierre Wertheimer, 59 Blvd Pinel, 69677 Bron CEDEX, France (jerome.honnorat@chu-lyon.fr).

Published Online: August 17, 2015. doi:10.1001/jamaneurol.2015.1715.

Author Contributions: Dr Honnorat had full access to all the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.

Study concept and design: Joubert, Zekeridou, Psimaras, Honnorat.

Acquisition, analysis, or interpretation of data: Joubert, Kerschen, Zekeridou, Ducray, Desestret, Rogemond, Chaffois, Larrue, Daubail, Idbaih, Antoine, Delattre, Honnorat.

Drafting of the manuscript: Joubert, Kerschen, Zekeridou, Rogemond, Antoine, Honnorat.

Critical revision of the manuscript for important intellectual content: Joubert, Zekeridou, Desestret, Chaffois, Ducray, Larrue, Daubail, Idbaih, Psimaras, Antoine, Delattre, Honnorat.

Statistical analysis: Ducray.

Administrative, technical, or material support: Zekeridou, Chaffois, Delattre.

Study supervision: Ducray, Larrue, Honnorat.

Conflict of Interest Disclosures: Dr Idbaih reported having financial interests unrelated to this work with Intsel Chimos (research funding), Hoffmann-La Roche (travel and meeting), Beta Innov (research funding), and Novartis (lecture). No other disclosures were reported.

Funding/Support: The Hospices Civils de Lyon, Institut National de la Santé et de la Récherche Médicale, and Neurobiotec biobank funded collection of the data and biological samples.

Role of the Funder/Sponsor: The funding sources had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication.

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